Stabilizing organo-siloxanes



Patented Nov. 27, 1945 Rob Roy McGregor, Verona, and Earl Leathen Warrick, Pittsburgh, Pa, asslgnorsto Corning Glass Works, Corning, N.

New York Y., a corporation of No Drawing. Application J une 22, 1944, Serial No. 541,669

7 Claims.

This. invention relates to organo-siloxanes, and particularly to the stabilization thereof.

This application is a continuation-in-part of our copending application, Serial Number 432,530, filed February 26, 1942, and assigned to the assignee of the present invention.

Organo-siloxanes are compositions comprising essentially silicon atoms connected to each other by oxygen atoms through silicon-oxygen linkages, thus and organic radicals attached through carbon silicon linkages to at least some of the silicen atoms. They may be prepared by the hydrolysis of a hydrolyzable organo-mono-silane followed by condensation (partial or complete) of the hydrolysis product. They may also be prepared by hydrolyzing and condensing mixtures of different hydrolyzable organo-monosilanes, as described in the copending application of James Franklin Hyde, Serial Number'432,528, filed February 26, 1942, and assigned to the assignee of the present invention. In the latter case, hydrolyzable silanes whichcontain no organic radicals attached to silicon through carbon-silicon linkages, such as silicon tetrachloride or ethyl orthosilicate, may be included with the organosilanes, if desired. By employing such mixtures of silanes, it is possible to prepare organo-siloxanes which contain on the average up to and including. three organic radicals per silicon atom. By hydrolyzable organo-monosilaneawe mean derivatives of SiI-Ia, which contain hydrolyzable radicals such as halogens, amino groups, alkoxy, aroxy and acyloxy radicals, etc., and organic radicals that are joined to silicon through carbonsilicon linkage. Examples of such organic radicals are as follows: aliphatic radicals such as, methyl, ethyl, propyl, isopropyl, butyl, amyl, hexyl, heptyl to octadecyl and higher; alicyclic radicals such as cyclopentyl, cyclohexyl, etc.: aryl and alkaryl radicals such as .phenyl, monoand poly-alkyl phenyls as tolyl, xylyl, mesityl,

thereof is generally accompanied by condensation of the intermediately formed hydroxy compounds to form siloxane linkages, thus aim-ii- The formation of a siloxane linkage generally results'from the close approach of two hydroxyl groups and subsequent elimination of water. It may also result from the close approach of one hydroxyl group to a hydrolyzable group such as halogen, acyloxy, or alkoxy, etc., and subsequent elimination of hydrogen halide, carboxylic acid or alcohol, respectively. Such eliminations are catalyzed by mineral acids, especially hydrochlo ric and sulphuric, and by alkali metal hydroxides, especially sodium hydroxide. As a result of the hydrolysis and condensation, organo-siloxanes are produced which are partially or com.- pletely condensed and which have on the average up to and including three organic radicals attached to each silicon atom. The organo-siloxanes, as previously mentioned, consist essentially of silicon atoms joined together by oxygen atoms through silicon-oxygen linkages and organic radicals attached to silicon through carbon-silicon linkages, the remaining valences, ii any, of the silicon atoms being satisfied by hydroxyl radicals and/or by residual unhydrolyzed radicals such as halogens, alkoxy,.etc. listed above as the hydrolyzable radicals.

The organo-siloxanes' so obtained, some of .which are liquids, others solids, differ with respect to their resistance to heat. In general, the partially condensed liquid siloxanes undergo a change in physical properties when heated, becoming more viscous, until finally they may become solids. On the other hand, those which are completely condensed, or nearly so (i. e. substantially free of hydroxyl groups) are extremely resistant to further change due to heat alone. However, even the latter may be further polymerized by contact with acidic agents, alkaline agents, or with air, as disclosed in the copending mono-, di-, and tri-ethyl phenyls, mono-, di-, and tri-propyl jphenyls, etc. naphthyl, monoand,

applications of James Franklin Hyde, Serial Number 481,155, filed March 30, 1943, Serial Number 481,154, filed March 30, 1943, and Serial Number 451,354, filed July 17, 1942, all being assigned to the assignee of the present invention.

All the organ'o-siloxanes, both solid and liquid, undergo a gradual change 'in properties when exposed to the combined eflect of heat and air for a prolonged period of time. This is true even of the completely condensed siloxanes. In the case or the liquid organo-siloxanes, the eflect of heat and air is manifested by an increase in viscosity, frequently followed by gelation. This is objectionable where the liquid is being utilized trarily chosen capillary pipette. The following table shows the viscosities in seconds after heating for various lengths oi. time.

TABLE I Viscosities after heating Hours at 230 0.

p-Amino-phenol p-Hydlrtolxyi-N-monobenzyl aniline.

NostabiliifIIIIIIIIIIIIII::1:

as a hydraulic fluid, dielectric medium and the like. The resinous solid siloxanes, after long exposure to oxygen at elevated temperatures, also undergo a change in properties, becoming less flexible and tough until eventually they reach an extremely brittle stage. Such changes in properties due to heat or to heat and air combined are obviously undesirable.

The primary object of this invention is to stabilize organo-siloxanes.

Another object is to provide a method by which changes of properties of organo-siloxanes due to heat and/or oxygen can be prevented.

Another object is to provide a stabilizer for organo-siloxanes.

We have discovered that the stability of an organo-siloxane may be substantially improved by incorporating therein a minor proportion of an aromatic compound having a hydroxyl group attached to the ring through a carbon atom. From 0.05 to preferably from 0.1 to 1.5% by weight of the stabilizer may be included in the composition to advantage. Although larger amounts of the stabilizer may be used, if desired, little advantage is gained thereby, as will be shown below. The so-formed stabilized composi tion exhibits a marked improvement in resistance to change under the influence of heat and air.

Among the stabilizers which may be employed in accordance with our invention are 3-methyl catechol, t-butyl catechol, cyclohexyl catechol, 4-phenyl catechol, 2-phenyl hydroquinone, 4- hydroxyphenyl benzyl ether, p-aminophenol, 4- hydroxydiphenyl amine, N-(4-hydroxy phenyl) morpholine, a-naphthol, fl-naphthol, pyrogallol, gallic acid, hydroquinone, dibutyl resorcinol, phenol, pyrocatechol, p-hydroxy-N-monobenzyl aniline, p-hydroxy-N,N-dibenzyl aniline, and resorcinol. In general, we prefer to employ those aromatic compounds having a plurality of hydroxyl groups attached to the ring, since they are outstanding in their stabilizing effect.

For a better understanding of the invention reference should be had to the following examples, which are given merely by way of illustration and are not to be construed as limiting.

EXAMIPLEI Individual portions of a liquid dimethyl siloxane, (prepared by the acid catalyzed hydrolysis oi dimethyldiethoxy silane) were treated by addition oi. 1% by weight of various stabilizers after which the diflerent portions were heated at 230 C. The viscosities oi the dimethyl silicone before and after heating for various lengths or time were determined by measuring the number oiseconds required for a given amoimt or the liquid at room temperature to flow from n i- It will be noted that the sample to which no stabilizer was added became solid in 48 hours, but samples containing a stabilizer remained liquid for over a month at this elevated temperature.

EXAMPLE 2 lowing table. Also .given in the table under the heading Slope are the values obtained by dividing the total viscosity increase up to the point oi incipient gelation by the total time in hours required to reach that point.

Team: II

Inhibitor Time, hrs. Slope It will be observed that the eii'ect of these hydroxy containing stabilizers is primarily to delay gelation and only secondarily to prevent viscosity increase- In this respect they are inferior to the organic amines which not only markedly delay gelation but also substantially restrain viscosity increase as shown in our copending application filed on even date herewith.

The use of the hydroxy containing stabilizers as stabilizers for organo-siloxanes is particularly important in the case of the liquid alkyl siloxanes such as ethyl siloxane, propyl siloxane, amyl siloxane, etc., and also the liquid aryl alkyl siloxanes such as phenyl methyl siloxane, phenyl ethyl siloxane, etc. The stabilizers are especially usetul when incorporated in siloxanes having on the average approximately one to approximately two organic radicals per silicon atom and especially those containing alkyl radicals since these are particularly sensitive to heat and air.

In general, the effectiveness oi the stabilizer is directly proportional to the amount added to the organo-siloxane. The following table demonstrates the stabilizing eflect of varying amounts of 3-methyl catechol on liquid dimethyl silicone. The first column lists the din'erent amounts oi inhibitor used in per cent by weight. The remaining columns give the per cent viscosity increase in different hours of heating at250 C.

hexyl catechol, pyrogallol, 2-phenyl hydroquinone, and 4-phenyl catechol, the organic substituents of said siloxane consisting essentially of Tears III Per cent viscosity increase-250 0.

Per cent 34 hr. 1% hr. 2% m. 4 hr. 6 hr. 8 hr. 10 hr. 12 hr. in m. 20 hr.

12 41 141 1,850 Gel 1 2 2 38 92 582 Gel .a 4 0 a 23 110 575 Gel .s e 2 11 as 210 486 G01 1.0 2 2 1o 15 a1 59 :30 Gel 1. 5 5 2 1o 13 2o 25 33 61 412 Gel In general, organo-siloxanes treated in accordance with our invention are more resistant to change in physical properties under the influence of heat and air. Specifically, the liquid organosiloxanes are thereby rendered more resistant to increase in viscosity or polymerization due to the effects of heat, the action of oxygen and catalysts in general. Because of their low pour points, small change of viscosity with temperature and inertness to rubber, they are useful as hydraulic fluids for the transmission of pressure, also as damping media for delicate instruments and recoil mechanisms or shock absorbing devices. The resinous solid organo-siloxanes when stabilized in accordance with our invention retain their flexibility and toughness for a greater length of time, and are thereby rendered more useful as electrically insulating coatings for metallic conductors, etc.

We claim:

1. The method of stabilizing an organo-siloxane which comprises incorporating therein stabilizing amounts of a polyhydroxy benzene selected from the class consisting of 3-methyl catechol, t-butyl catechol, cyclohexyl catechol, pyrogallol, 2-phenyl hydroquinone, and 4-phenyl catechol, the organic substituents of said siloxane consisting essentially of monovalent hydrocarbon radicals attached to silicon through carbon-silicon linkages.

2. A composition of matter comprising an organo-siloxane and a minor proportion of a polyhydroxy benzene selected from the class consisting of S-methyl catechol, t-butyl catechol, cyclomonovalent hydrocarbon radicals attached to silicon through carbon-silicon linkages.

3. A composition of matter comprising a liquid polymeric organo-siloxane and a minor proportion of a polyhydroxy benzene selected from the class consisting of S-methyl catechol, t-butyl catechol, cyclohexyl catechol, pyrogallol, 2-phenyl hydroquinone, and 4-phenyl catechol, said organo-siloxane having on the average from approximately 1 to approximately 2 monovalent hydrocarbon radicals attached to each silicon atom through carbon-silicon linkages, at least some of said hydrocarbon radicals being alkyl radicals.

4. A composition of matter comprising a liquid organo-siloxane comprising essentially structural units of the formula (CH3) 2510 and a minor proportion of a polyhydroxy benzene selected from the class consisting of 3-methyl catechol, t-butyl catechol, cyclohexyl catechol, pyrogallol, 2- phenyl hydroquinone, and 4-phenyl catechol.

5. A composition of matter comprising a liquid methyl siloxane comprising essentially structural units of the formula (CHa)2SiO and a minor proportion of 3-methyl catechol.

6. A composition of matter comprising a liquid methyl siloxane comprising essentially structural units of the formula (CH3) :SiO and a minor proportion of t-butyl catechol.

7. A composition of matter comprising a liquid methyl siloxane comprising essentially structural units of the formula (CI-L1) 2810 and a minor proportion of 4-phenyl catechol.

ROB ROY McGREGOIt.- EARL LEATHEN WABRICK. 

